AGPS

AGPS or assisted GPS is a variant of GPS used in cell phones. It uses an assistance server to cut down the time needed to find the location.

In a self-contained GPS receiver, the receiver contains such pieces a radio, signal processor, geospatial almanac, conversion functions, and optional positional reference data (e.g. maps), all of which together provide the viewing user with understandable information about their position e.g. latitude and longitude.

In AGPS however, the handheld device only (necessarily) contains a radio and signal processor. The results of the GPS signal receipt and processing are then passed over the wireless network, to be interpreted by the assistance server located elsewhere. The assistance server then performs the necessary math and conversions to determine the map location of the handheld.

This method minimizes the amount of memory and hardware that must be integrated into mobile devices in order to provide GPS-quality device locating ability as required by E911.